Green manures are particular plants which are grown to improve the structure and/or the fertility of the soil. They break up heavy soils and improve drainage, and can help light soils hold more water. Different green manures have roots of differing depths. These can mine for different minerals in the soil, bring them to the surface and keep them there. Green manures of the Legume family increase Nitrogen in the soil which will be available to the following crop in the form of nitrates. Some, such as Alfalfa, root down very deep and bring up minerals to the top layer of the soil. The green tops of Green manures, when dug in, add humus and nutrients.
MAIN GROWING SEASON
A quick-growing Green manure such as Mustard can be sown mid-season before sowing a second vegetable crop on that patch of ground.
Sow a Green manure that will keep the ground covered and protected over the winter (such as Red Clover, Alfalfa, Vetch (Tares), or Phacelia). This will help prevent the leaching of nutrients during the winter months. The plants can then be dug into the soil in March. On an allotment, Red Clover or Alfalfa can be sown in rows widely spaced, clipped several times a season to stop them from flowering, and a crop can be grown between these rows. The Green manure clippings then form a good mulch to maintain moisture, while at the same time their roots are ‘feeding’ the growing crop.
Dig in when plants are fresh and green. Does well in dry conditions. Dislikes acid or waterlogged soils. Can overwinter from a late sowing. A very deep rooter. Foliage contains an excellent range of plant foods. Fixes nitrogen. Alfalfa can be grown for a few months or for a year or two. If grown long term, cut down 2 or 3 times a year to encourage new growth. Sow April to July. 2 to 3g per sq. metre. Winter hardy. Coverage 45 sq.m
Vigorous quick growing clover with deep red flowers very attractive to bees. Grows best on sandy loam soil. Grow as annual March to August. Will overwinter from an August sowing in the southern counties of UK. Sow April to August. 1.5g to 3g per sq. metre. Winter hardy in the south. Coverage 30sq.m
A deep-rooting bushy clover with red flowers which bees love. Not a creeping clover. Prefers a good loam, not too acidic with a pH above 5.5. Can be sown for a few months, or for a year or two. If grown long term, cut down when flowering to encourage new growth. Fixes Nitrogen. Sow April to August. 1.5g to 3g per sq. metre. Winter hardy. Coverage 30 sq.m
An attractive quick-growing bushy plant with small white flowers and a mass of foliage. Dig in any time up to flowering. Does best on well-drained but slightly heavy soils. Will tolerate lighter ones if reasonably moist. An annual which is quick to start. Grow for up to 2 to 3 months. Unlikely to fix Nitrogen in the UK. Sow April to July, thinly in 15cm rows. 5g per sq. metre. Coverage 20 sq.m
One of the fastest growing green manures. Yellow flowers. Needs a reasonably moist and fertile soil, especially in the top 5cm. Chop in with a spade any time up to flowering. This can be from 2 to 8 weeks. Once flowers begin to form it goes tough very quickly. Susceptible to clubroot. Sow March to August, thinly in 15cm rows. 3g to 5g per sq. metre. Coverage 20 sq. m
A lovely bushy plant with masses of ferny foliage and bright blue flowers loved by bees. An annual which is quick to start. Grow for up to 2 months in summer, 5 to 6 months over winter. September-sown plants will overwinter to be dug in during the spring. Dig in before flowers open and before stems get woody. Can be clipped to add foliage to the soil. Keeps weeds down well. Seed is quite expensive but if some plants are left to flower, seed can be easily saved for another season. Usually winter hardy. Sow April to August, thinly in 20cm rows. 2g to 3g per sq. metre. Coverage 25 sq.m
Known also as TARES. A rapid growing annual vetch. Good bushy plants. Prefers slightly heavy soils. Will not thrive on dry or acid soils. Grow for 2 to 3 months in summer. Can be overwintered from a late sowing. Dig in any time up to flowering. Slow to start from an autumn sowing so avoid weedy sites at this time, or keep weeds hoed out. Can be mixed with Ryegrass. Fixes Nitrogen. Sow March to May, July to end August, thinly in 15cm rows. Winter hardy. 20g per sq.m. Sow 4-5cm deep. Not for broadcasting. Coverage 7 sq.m